Communication device, processing device and method for transmitting data unit

ABSTRACT

A communication device, processing device or method constructs M RLC PDUs including M RLC SDUs, respectively, where M is larger than 1; submits, for a transmission opportunity, only L RLC PDUs for L RLC SDUs with lowest L SNs among the M RLC PDUs to a MAC layer, where L&lt;M and the L RLC PDUs include a first RLC PDU having a poll to trigger status reporting at a receiving device; transmits the L RLC PDUs to the receiving device; constructs a second RLC PDU including a second RLC SDU having a highest SN among SNs of RLC SDUs submitted to the MAC layer, when the poll retransmission timer started upon submitting the first RLC PDU having the poll expires and no new RLC SDU or RLC SDU segment can be transmitted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/KR2019/000189, filed on Jan. 7, 2019, which claims the benefit ofU.S. Provisional Application No. 62/614,484, filed on Jan. 7, 2018. Thedisclosures of the prior applications are incorporated by reference intheir entirety.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system.

BACKGROUND ART

As an example of a mobile communication system to which the presentdisclosure is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a diagram illustrating an example of a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aUniversal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist per eNB. The cell is set to operate in oneof bandwidths such as 1.25, 2.5, 5, 10, 15, and 20 MHz and provides adownlink (DL) or uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be set to provide differentbandwidths. The eNB controls data transmission or reception to and froma plurality of UEs. The eNB transmits DL scheduling information of DLdata to a corresponding UE so as to inform the UE of a time/frequencydomain in which the DL data is supposed to be transmitted, coding, adata size, and hybrid automatic repeat and request (HARM)-relatedinformation. In addition, the eNB transmits UL scheduling information ofUL data to a corresponding UE so as to inform the UE of a time/frequencydomain which may be used by the UE, coding, a data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A core network (CN) mayinclude the AG and a network node or the like for user registration ofUEs. The AG manages the mobility of a UE on a tracking area (TA) basis.One TA includes a plurality of cells.

DISCLOSURE Technical Problem

Introduction of new radio communication technologies has led toincreases in the number of user equipments (UEs) to which a base station(BS) provides services in a prescribed resource region, and has also ledto increases in the amount of data and control information that the BStransmits to the UEs. Due to typically limited resources available tothe BS for communication with the UE(s), new techniques are needed bywhich the BS utilizes the limited radio resources to efficientlyreceive/transmit uplink/downlink data and/or uplink/downlink controlinformation. In particular, overcoming delay or latency has become animportant challenge in applications whose performance critically dependson delay/latency.

The technical objects that can be achieved through the present inventionare not limited to what has been particularly described hereinabove andother technical objects not described herein will be more clearlyunderstood by persons skilled in the art from the following detaileddescription.

Technical Solution

In an aspect of the present disclosure, provided herein is acommunication device for transmitting a data unit in a wirelesscommunication system. The communication device comprises a transceiver,and a processor configured to control the transceiver. The processor isconfigured to: construct M radio link control (RLC) protocol data units(PDUs) including M RLC service data units (SDUs), respectively, where Mis larger than 1; submit, for a transmission opportunity, only L RLCPDUs for L RLC SDUs with lowest L sequence numbers (SNs) among the M RLCPDUs to a medium access control (MAC) layer, where L<M and the L RLCPDUs include a first RLC PDU having a poll to trigger status reportingat a receiving device; start a poll retransmission timer upon submittingthe first RLC PDU having the poll to the MAC layer; control thetransceiver to transmit the L RLC PDUs to the receiving device;construct a second RLC PDU including a second RLC SDU having a highestSN among SNs of RLC SDUs submitted to the MAC layer, when the pollretransmission timer expires and no new RLC SDU or RLC SDU segment canbe transmitted; and control the transceiver to transmit the second RLCPDU including the second RLC SDU.

In another aspect of the present disclosure, provided herein is aprocessing device comprising: at least one processor; and at least onecomputer memory that is operably connectable to the at least oneprocessor and that has stored thereon instructions which, when executed,cause the at least one processor to perform operations. The operationscomprises: constructing M radio link control (RLC) protocol data units(PDUs) including M RLC service data units (SDUs), respectively, where Mis larger than 1; submitting, for a transmission opportunity, only L RLCPDUs for L RLC SDUs with lowest L sequence numbers (SNs) among the M RLCPDUs to a medium access control (MAC) layer, where L<M and the L RLCPDUs include a first RLC PDU having a poll to trigger status reportingat a receiving device; start a poll retransmission timer upon submittingthe first RLC PDU having the poll to the MAC layer; transmitting the LRLC PDUs to the receiving device; constructing a second RLC PDUincluding a second RLC SDU having a highest SN among SNs of RLC SDUssubmitted to the MAC layer, when the poll retransmission timer expiresand no new RLC SDU can be transmitted; and transmitting the second RLCPDU including the second RLC SDU.

In a further aspect of the present disclosure, provided herein is amethod for transmitting a data unit by a communication device in awireless communication system. The method comprises: constructing Mradio link control (RLC) protocol data units (PDUs) including M RLCservice data units (SDUs), respectively, where M is larger than 1;submitting, for a transmission opportunity, only L RLC PDUs for L RLCSDUs with lowest L sequence numbers (SNs) among the M RLC PDUs to amedium access control (MAC) layer, where L<M and the L RLC PDUs includea first RLC PDU having a poll to trigger status reporting at a receivingdevice; start a poll retransmission timer upon submitting the first RLCPDU having the poll to the MAC layer; transmitting the L RLC PDUs to thereceiving device; constructing a second RLC PDU including a second RLCSDU having a highest SN among SNs of RLC SDUs submitted to the MAClayer, when the poll retransmission timer expires and no new RLC SDU canbe transmitted; and transmitting the second RLC PDU including the secondRLC SDU.

In each aspect of the present disclosure, a poll may be included in thesecond RLC PDU.

In each aspect of the present disclosure, a state variable may be set to1+a highest SN among SNs of the M RLC PDUs. The state variable holds anSN to be assigned for a newly generated RLC PDU and is updated wheneveran RLC PDU with an SN=the state variable, which includes an RLC SDU or alast segment of an RLC SDU, is constructed.

In each aspect of the present disclosure, a MAC PDU including the L RLCPDUs may be constructed. The MAC PDU including the L RLC PDUs may betransmitted in the transmission opportunity.

In each aspect of the present disclosure, the highest SN among the SNsof the RLC SDUs submitted to the MAC layer is smaller than a highest SNamong SNs of the M RLC SDUs.

The above technical solutions are merely some parts of theimplementations of the present disclosure and various implementationsinto which the technical features of the present disclosure areincorporated can be derived and understood by persons skilled in the artfrom the following detailed description of the present disclosure.

Advantageous Effects

In some scenarios, implementations of the present disclosure may provideone or more of the following advantages. In some scenarios, radiocommunication signals can be more efficiently transmitted and/orreceived. Therefore, overall throughput of a radio communication systemcan be improved.

According to some implementations of the present disclosure,delay/latency occurring during communication between a user equipmentand a BS may be reduced.

Also, signals in a new radio access technology system can be transmittedand/or received more effectively.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved through the present disclosure are not limited towhat has been particularly described hereinabove and other advantages ofthe present disclosure will be more clearly understood from thefollowing detailed description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention:

FIG. 1 is a diagram illustrating an example of a network structure of anevolved universal mobile telecommunication system (E-UMTS) as anexemplary radio communication system;

FIG. 2 is a block diagram illustrating an example of an evolveduniversal terrestrial radio access network (E-UTRAN);

FIG. 3 is a block diagram depicting an example of an architecture of atypical E-UTRAN and a typical EPC;

FIG. 4 illustrates an example of protocol stacks of the 3GPP basedcommunication system;

FIG. 5 illustrates an example of a frame structure in the 3GPP basedwireless communication system;

FIG. 6 illustrates an example of a data flow in the 3GPP LTE system;

FIG. 7 illustrates an example of a data flow in the 3GPP NR system;

FIG. 8 illustrates a model of an acknowledged mode (AM) radio linkcontrol (RLC) entity in the 3GPP LTE system;

FIG. 9 illustrates a model of AM RLC entity which can be used in theimplementation(s) of the present disclosure;

FIGS. 10A and 10B illustrate examples of data transfer according to theimplementations of the present disclosure; and

FIG. 11 is a block diagram illustrating examples of communicationdevices which can perform method(s) of the present disclosure.

MODE FOR INVENTION

Although wireless communication technology has been developed to LTEbased on wideband code division multiple access (WCDMA), the demands andexpectations of users and service providers are on the rise. Inaddition, considering other radio access technologies under development,new technological evolution is required to secure high competitivenessin the future. Decrease in cost per bit, increase in serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, and the likeare required.

As more and more communication devices demand larger communicationcapacity, there is a need for improved mobile broadband communicationcompared to existing RAT. Also, massive machine type communication(MTC), which provides various services by connecting many devices andobjects, is one of the major issues to be considered in the nextgeneration communication. In addition, a communication system designconsidering a service/UE sensitive to reliability and latency is beingdiscussed. The introduction of next-generation RAT, which takes intoaccount such advanced mobile broadband communication, massive MTC(mMCT), and ultra-reliable and low latency communication (URLLC), isbeing discussed.

Reference will now be made in detail to the exemplary implementations ofthe present disclosure, examples of which are illustrated in theaccompanying drawings. The detailed description, which will be givenbelow with reference to the accompanying drawings, is intended toexplain exemplary implementations of the present disclosure, rather thanto show the only implementations that can be implemented according tothe disclosure. The following detailed description includes specificdetails in order to provide a thorough understanding of the presentdisclosure. However, it will be apparent to those skilled in the artthat the present disclosure may be practiced without such specificdetails.

The following techniques, apparatuses, and systems may be applied to avariety of wireless multiple access systems. Examples of the multipleaccess systems include a code division multiple access (CDMA) system, afrequency division multiple access (FDMA) system, a time divisionmultiple access (TDMA) system, an orthogonal frequency division multipleaccess (OFDMA) system, a single carrier frequency division multipleaccess (SC-FDMA) system, and a multicarrier frequency division multipleaccess (MC-FDMA) system. CDMA may be embodied through radio technologysuch as universal terrestrial radio access (UTRA) or CDMA2000. TDMA maybe embodied through radio technology such as global system for mobilecommunications (GSM), general packet radio service (GPRS), or enhanceddata rates for GSM evolution (EDGE). OFDMA may be embodied through radiotechnology such as institute of electrical and electronics engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or evolved UTRA(E-UTRA). UTRA is a part of a universal mobile telecommunications system(UMTS). 3rd generation partnership project (3GPP) long term evolution(LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employsOFDMA in DL and SC-FDMA in UL. LTE-advanced (LTE-A) is an evolvedversion of 3GPP LTE. For convenience of description, implementations ofthe present disclosure are described in regards to a 3GPP based wirelesscommunication system. However, the technical features of the presentdisclosure are not limited thereto. For example, although the followingdetailed description is given based on a mobile communication systemcorresponding to a 3GPP based system, aspects of the present disclosurethat are not limited to 3GPP based system are applicable to other mobilecommunication systems.

For example, the present disclosure is applicable to contention basedcommunication such as Wi-Fi as well as non-contention basedcommunication as in the 3GPP based system in which a BS allocates aDL/UL time/frequency resource to a UE and the UE receives a DL signaland transmits a UL signal according to resource allocation of the BS. Ina non-contention based communication scheme, an access point (AP) or acontrol node for controlling the AP allocates a resource forcommunication between the UE and the AP, whereas, in a contention basedcommunication scheme, a communication resource is occupied throughcontention between UEs which desire to access the AP. The contentionbased communication scheme will now be described in brief. One type ofthe contention based communication scheme is carrier sense multipleaccess (CSMA). CSMA refers to a probabilistic media access control (MAC)protocol for confirming, before a node or a communication devicetransmits traffic on a shared transmission medium (also called a sharedchannel) such as a frequency band, that there is no other traffic on thesame shared transmission medium. In CSMA, a transmitting devicedetermines whether another transmission is being performed beforeattempting to transmit traffic to a receiving device. In other words,the transmitting device attempts to detect presence of a carrier fromanother transmitting device before attempting to perform transmission.Upon sensing the carrier, the transmitting device waits for anothertransmission device which is performing transmission to finishtransmission, before performing transmission thereof. Consequently, CSMAcan be a communication scheme based on the principle of “sense beforetransmit” or “listen before talk”. A scheme for avoiding collisionbetween transmitting devices in the contention based communicationsystem using CSMA includes carrier sense multiple access with collisiondetection (CSMA/CD) and/or carrier sense multiple access with collisionavoidance (CSMA/CA). CSMA/CD is a collision detection scheme in a wiredlocal area network (LAN) environment. In CSMA/CD, a personal computer(PC) or a server which desires to perform communication in an Ethernetenvironment first confirms whether communication occurs on a networkand, if another device carries data on the network, the PC or the serverwaits and then transmits data. That is, when two or more users (e.g.PCs, UEs, etc.) simultaneously transmit data, collision occurs betweensimultaneous transmission and CSMA/CD is a scheme for flexiblytransmitting data by monitoring collision. A transmitting device usingCSMA/CD adjusts data transmission thereof by sensing data transmissionperformed by another device using a specific rule. CSMA/CA is a MACprotocol specified in IEEE 802.11 standards. A wireless LAN (WLAN)system conforming to IEEE 802.11 standards does not use CSMA/CD whichhas been used in IEEE 802.3 standards and uses CA, i.e. a collisionavoidance scheme. Transmission devices always sense carrier of a networkand, if the network is empty, the transmission devices wait fordetermined time according to locations thereof registered in a list andthen transmit data. Various methods are used to determine priority ofthe transmission devices in the list and to reconfigure priority. In asystem according to some versions of IEEE 802.11 standards, collisionmay occur and, in this case, a collision sensing procedure is performed.A transmission device using CSMA/CA avoids collision between datatransmission thereof and data transmission of another transmissiondevice using a specific rule.

For terms and technologies which are not specifically described amongthe terms of and technologies employed in the present disclosure, thewireless communication standard documents published before the presentdisclosure may be referenced. For example, the following documents maybe referenced.

3GPP LTE

3GPP TS 36.211: Physical channels and modulation

3GPP TS 36.212: Multiplexing and channel coding

3GPP TS 36.213: Physical layer procedures

3GPP TS 36.214: Physical layer; Measurements

3GPP TS 36.300: Overall description

3GPP TS 36.304: User Equipment (UE) procedures in idle mode

3GPP TS 36.314: Layer 2—Measurements

3GPP TS 36.321: Medium Access Control (MAC) protocol

3GPP TS 36.322: Radio Link Control (RLC) protocol

3GPP TS 36.323: Packet Data Convergence Protocol (PDCP)

3GPP TS 36.331: Radio Resource Control (RRC) protocol

3GPP NR

3GPP TS 38.211: Physical channels and modulation

3GPP TS 38.212: Multiplexing and channel coding

3GPP TS 38.213: Physical layer procedures for control

3GPP TS 38.214: Physical layer procedures for data

3GPP TS 38.215: Physical layer measurements

3GPP TS 38.300: Overall description

3GPP TS 38.304: User Equipment (UE) procedures in idle mode and in RRCinactive state

3GPP TS 38.321: Medium Access Control (MAC) protocol

3GPP TS 38.322: Radio Link Control (RLC) protocol

3GPP TS 38.323: Packet Data Convergence Protocol (PDCP)

3GPP TS 38.331: Radio Resource Control (RRC) protocol

3GPP TS 37.324: Service Data Adaptation Protocol (SDAP)

3GPP TS 37.340: Multi-connectivity; Overall description

In the present disclosure, a user equipment (UE) may be a fixed ormobile device. Examples of the UE include various devices that transmitand receive user data and/or various kinds of control information to andfrom a base station (BS). The UE may be referred to as a terminalequipment (TE), a mobile station (MS), a mobile terminal (MT), a userterminal (UT), a subscriber station (SS), a wireless device, a personaldigital assistant (PDA), a wireless modem, a handheld device, etc. Inaddition, in the present disclosure, a BS generally refers to a fixedstation that performs communication with a UE and/or another BS, andexchanges various kinds of data and control information with the UE andanother BS. The BS may be referred to as an advanced base station (ABS),a node-B (NB), an evolved node-B (eNB), a base transceiver system (BTS),an access point (AP), a processing server (PS), etc. Especially, a BS ofthe UMTS is referred to as a NB, a BS of the EPC/LTE is referred to asan eNB, and a BS of the new radio (NR) system is referred to as a gNB.

In the present disclosure, a node refers to a fixed point capable oftransmitting/receiving a radio signal through communication with a UE.Various types of BSs may be used as nodes irrespective of the termsthereof. For example, a BS, a node B (NB), an e-node B (eNB), apico-cell eNB (PeNB), a home eNB (HeNB), a relay, a repeater, etc. maybe a node. In addition, the node may not be a BS. For example, the nodemay be a radio remote head (RRH) or a radio remote unit (RRU). The RRHor RRU generally has a lower power level than a power level of a BS.Since the RRH or RRU (hereinafter, RRH/RRU) is generally connected tothe BS through a dedicated line such as an optical cable, cooperativecommunication between RRH/RRU and the BS can be smoothly performed incomparison with cooperative communication between BSs connected by aradio line. At least one antenna is installed per node. The antenna mayinclude a physical antenna or an antenna port or a virtual antenna.

In the present disclosure, the term “cell” may refer to a geographicarea to which one or more nodes provide a communication system, or referto radio resources. A “cell” of a geographic area may be understood ascoverage within which a node can provide service using a carrier and a“cell” as radio resources (e.g. time-frequency resources) is associatedwith bandwidth (BW) which is a frequency range configured by thecarrier. The “cell” associated with the radio resources is defined by acombination of downlink resources and uplink resources, for example, acombination of a downlink (DL) component carrier (CC) and a uplink (UL)CC. The cell may be configured by downlink resources only, or may beconfigured by downlink resources and uplink resources. Since DLcoverage, which is a range within which the node is capable oftransmitting a valid signal, and UL coverage, which is a range withinwhich the node is capable of receiving the valid signal from the UE,depends upon a carrier carrying the signal, the coverage of the node maybe associated with coverage of the “cell” of radio resources used by thenode. Accordingly, the term “cell” may be used to represent servicecoverage of the node sometimes, radio resources at other times, or arange that signals using the radio resources can reach with validstrength at other times.

In carrier aggregation (CA), two or more CCs are aggregated. A UE maysimultaneously receive or transmit on one or multiple CCs depending onits capabilities. CA is supported for both contiguous and non-contiguousCCs. When CA is configured the UE only has one radio resource control(RRC) connection with the network. At RRC connectionestablishment/re-establishment/handover, one serving cell provides thenon-access stratum (NAS) mobility information, and at RRC connectionre-establishment/handover, one serving cell provides the security input.This cell is referred to as the Primary Cell (PCell). The PCell is acell, operating on the primary frequency, in which the UE eitherperforms the initial connection establishment procedure or initiates theconnection re-establishment procedure. Depending on UE capabilities,Secondary Cells (SCells) can be configured to form together with thePCell a set of serving cells. An SCell is a cell providing additionalradio resources on top of Special Cell. The configured set of servingcells for a UE therefore always consists of one PCell and one or moreSCells. For dual connectivity operation, the term Special Cell (SpCell)refers to the PCell of the master cell group (MCG) or the PSCell of thesecondary cell group (SCG). An SpCell supports PUCCH transmission andcontention-based random access, and is always activated. The MCG is agroup of serving cells associated with a master node, comprising of theSpCell (PCell) and optionally one or more SCells. The SCG is the subsetof serving cells associated with a secondary node, comprising of thePSCell and zero or more SCells, for a UE configured with dualconnectivity (DC). For a UE in RRC CONNECTED not configured with CA/DCthere is only one serving cell comprising of the PCell. For a UE in RRCCONNECTED configured with CA/DC the term “serving cells” is used todenote the set of cells comprising of the SpCell(s) and all SCells. InDC, two MAC entities are configured in a UE: one for the MCG and one forthe SCG.

In the present disclosure, “PDCCH” may refer to a PDCCH, an EPDCCH (insubframes when configured), a MTC PDCCH (MPDCCH), for an RN with R-PDCCHconfigured and not suspended, to the R-PDCCH or, for NB-IoT to thenarrowband PDCCH (NPDCCH).

In the present disclosure, monitoring a channel refers to attempting todecode the channel. For example, monitoring a PDCCH refers to attemptingto decode PDCCH(s) (or PDCCH candidates).

In the present disclosure, for dual connectivity (DC) operation, theterm “special Cell” refers to the PCell of the master cell group (MCG)or the PSCell of the secondary cell group (SCG), and otherwise the termSpecial Cell refers to the PCell. The MCG is a group of serving cellsassociated with a master BS which terminates at least S1-MME, and theSCG is a group of serving cells associated with a secondary BS that isproviding additional radio resources for the UE but is not the masterBS. The SCG includes a primary SCell (PSCell) and optionally one or moreSCells. In dual connectivity, two MAC entities are configured in the UE:one for the MCG and one for the SCG. Each MAC entity is configured byRRC with a serving cell supporting PUCCH transmission and contentionbased Random Access. In this specification, the term SpCell refers tosuch cell, whereas the term SCell refers to other serving cells. Theterm SpCell either refers to the PCell of the MCG or the PSCell of theSCG depending on if the MAC entity is associated to the MCG or the SCG,respectively.

In the present disclosure, “C-RNTI” refers to a cell RNTI, “SI-RNTI”refers to a system information RNTI, “P-RNTI” refers to a paging RNTI,“RA-RNTI” refers to a random access RNTI, “SC-RNTI” refers to a singlecell RNTI”, “SL-RNTI” refers to a sidelink RNTI, “SPS C-RNTI” refers toa semi-persistent scheduling C-RNTI, and “CS-RNTI” refers to aconfigured scheduling RNTI.

FIG. 2 is a block diagram illustrating an example of an evolveduniversal terrestrial radio access network (E-UTRAN). The E-UMTS may bealso referred to as an LTE system. The communication network is widelydeployed to provide a variety of communication services such as voice(VoIP) through IMS and packet data.

As illustrated in FIG. 2, the E-UMTS network includes an evolved UMTSterrestrial radio access network (E-UTRAN), an Evolved Packet Core (EPC)and one or more user equipment. The E-UTRAN may include one or moreevolved NodeB (eNodeB) 20, and a plurality of user equipments (UE) 10may be located in one cell. One or more E-UTRAN mobility managemententity (MME)/system architecture evolution (SAE) gateways 30 may bepositioned at the end of the network and connected to an externalnetwork.

As used herein, “downlink” refers to communication from BS 20 to UE 10,and “uplink” refers to communication from the UE to a BS.

FIG. 3 is a block diagram depicting an example of an architecture of atypical E-UTRAN and a typical EPC.

As illustrated in FIG. 3, an eNB 20 provides end points of a user planeand a control plane to the UE 10. MME/SAE gateway 30 provides an endpoint of a session and mobility management function for UE 10. The eNBand MME/SAE gateway may be connected via an S1 interface.

The eNB 20 is generally a fixed station that communicates with a UE 10,and may also be referred to as a base station (BS) or an access point.One eNB 20 may be deployed per cell. An interface for transmitting usertraffic or control traffic may be used between eNBs 20.

The MME provides various functions including NAS signaling to eNBs 20,NAS signaling security, access stratum (AS) Security control, Inter CNnode signaling for mobility between 3GPP access networks, Idle mode UEReachability (including control and execution of paging retransmission),Tracking Area list management (for UE in idle and active mode), PDN GWand Serving GW selection, MME selection for handovers with MME change,SGSN selection for handovers to 2G or 3G 3GPP access networks, roaming,authentication, bearer management functions including dedicated bearerestablishment, support for PWS (which includes ETWS and CMAS) messagetransmission. The SAE gateway host provides assorted functions includingPer-user based packet filtering (by e.g. deep packet inspection), LawfulInterception, UE IP address allocation, Transport level packet markingin the downlink, UL and DL service level charging, gating and rateenforcement, DL rate enforcement based on APN-AMBR. For clarity MME/SAEgateway 30 will be referred to herein simply as a “gateway,” but it isunderstood that this entity includes both an MME and an SAE gateway.

A plurality of nodes may be connected between eNB 20 and gateway 30 viathe S1 interface. The eNBs 20 may be connected to each other via an X2interface and neighboring eNBs may have a meshed network structure thathas the X2 interface.

As illustrated, eNB 20 may perform functions of selection for gateway30, routing toward the gateway during a Radio Resource Control (RRC)activation, scheduling and transmitting of paging messages, schedulingand transmitting of Broadcast Channel (BCCH) information, dynamicallocation of resources to UEs 10 in both uplink and downlink,configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE-IDLE state management,ciphering of the user plane, System Architecture Evolution (SAE) bearercontrol, and ciphering and integrity protection of Non-Access Stratum(NAS) signaling.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW), and a packet data network-gateway (PDN-GW). The MME hasinformation about connections and capabilities of UEs, mainly for use inmanaging the mobility of the UEs. The S-GW is a gateway having theE-UTRAN as an end point, and the PDN-GW is a gateway having a packetdata network (PDN) as an end point.

A fully mobile and connected society is expected in the near future,which will be characterized by a tremendous amount of growth inconnectivity, traffic volume and a much broader range of usagescenarios. Some typical trends include explosive growth of data traffic,great increase of connected devices and continuous emergence of newservices. Besides the market requirements, the mobile communicationsociety itself also requires a sustainable development of theeco-system, which produces the needs to further improve systemefficiencies, such as spectrum efficiency, energy efficiency,operational efficiency and cost efficiency. To meet the aboveever-increasing requirements from market and mobile communicationsociety, next generation access technologies are expected to emerge inthe near future.

Building upon its success of IMT-2000 (3G) and IMT-Advanced (4G), 3GPPhas been devoting its effort to IMT-2020 (5G) development sinceSeptember 2015. 5G New Radio (NR) is expected to expand and supportdiverse use case scenarios and applications that will continue beyondthe current IMT-Advanced standard, for instance, enhanced MobileBroadband (eMBB), Ultra Reliable Low Latency Communication (URLLC) andmassive Machine Type Communication (mMTC). eMBB is targeting high datarate mobile broadband services, such as seamless data access bothindoors and outdoors, and augmented reality (AR)/virtual reality (VR)applications; URLLC is defined for applications that have stringentlatency and reliability requirements, such as vehicular communicationsthat can enable autonomous driving and control network in industrialplants; mMTC is the basis for connectivity in IoT, which allows forinfrastructure management, environmental monitoring, and healthcareapplications.

FIG. 4 illustrates an example of protocol stacks in a 3GPP basedwireless communication system.

In particular, FIG. 4(a) illustrates an example of a radio interfaceuser plane protocol stack between a UE and a base station (BS) and FIG.4(b) illustrates an example of a radio interface control plane protocolstack between a UE and a BS. The control plane refers to a path throughwhich control messages used to manage call by a UE and a network aretransported. The user plane refers to a path through which datagenerated in an application layer, for example, voice data or Internetpacket data are transported. Referring to FIG. 4(a), the user planeprotocol stack may be divided into a first layer (Layer 1) (i.e., aphysical (PHY) layer) and a second layer (Layer 2). Referring to FIG.4(b), the control plane protocol stack may be divided into Layer 1(i.e., a PHY layer), Layer 2, Layer 3 (e.g., a radio resource control(RRC) layer), and a non-access stratum (NAS) layer. Layer 1, Layer 2 andLayer 3 are referred to as an access stratum (AS).

In the 3GPP LTE system, the layer 2 is split into the followingsublayers: Medium Access Control (MAC), Radio Link Control (RLC), andPacket Data Convergence Protocol (PDCP). In the 3GPP New Radio (NR)system, the layer 2 is split into the following sublayers: MAC, RLC,PDCP and SDAP. The PHY layer offers to the MAC sublayer transportchannels, the MAC sublayer offers to the RLC sublayer logical channels,the RLC sublayer offers to the PDCP sublayer RLC channels, the PDCPsublayer offers to the SDAP sublayer radio bearers. The SDAP sublayeroffers to 5G Core Network QoS flows.

In the 3GPP NR system, the main services and functions of SDAP include:mapping between a QoS flow and a data radio bearer; marking QoS flow ID(QFI) in both DL and UL packets. A single protocol entity of SDAP isconfigured for each individual PDU session.

In the 3GPP NR system, the main services and functions of the RRCsublayer include: broadcast of system information related to AS and NAS;paging initiated by 5GC or NG-RAN; establishment, maintenance andrelease of an RRC connection between the UE and NG-RAN; securityfunctions including key management; establishment, configuration,maintenance and release of Signaling Radio Bearers (SRBs) and Data RadioBearers (DRBs); mobility functions (including: handover and contexttransfer; UE cell selection and reselection and control of cellselection and reselection; Inter-RAT mobility); QoS managementfunctions; UE measurement reporting and control of the reporting;detection of and recovery from radio link failure; NAS message transferto/from NAS from/to UE.

In the 3GPP NR system, the main services and functions of the PDCPsublayer for the user plane include: sequence numbering; headercompression and decompression: ROHC only; transfer of user data;reordering and duplicate detection; in-order delivery; PDCP PDU routing(in case of split bearers); retransmission of PDCP SDUs; ciphering,deciphering and integrity protection; PDCP SDU discard; PDCPre-establishment and data recovery for RLC AM; PDCP status reporting forRLC AM; duplication of PDCP PDUs and duplicate discard indication tolower layers. The main services and functions of the PDCP sublayer forthe control plane include: sequence numbering; ciphering, decipheringand integrity protection; transfer of control plane data; reordering andduplicate detection; in-order delivery; duplication of PDCP PDUs andduplicate discard indication to lower layers.

In the 3GPP NR system, the RLC sublayer supports three transmissionmodes: Transparent Mode (TM); Unacknowledged Mode (UM); and AcknowledgedMode (AM). The RLC configuration is per logical channel with nodependency on numerologies and/or transmission durations. In the 3GPP NRsystem, the main services and functions of the RLC sublayer depend onthe transmission mode and include: Transfer of upper layer PDUs;sequence numbering independent of the one in PDCP (UM and AM); errorcorrection through ARQ (AM only); segmentation (AM and UM) andre-segmentation (AM only) of RLC SDUs; reassembly of SDU (AM and UM);duplicate detection (AM only); RLC SDU discard (AM and UM); RLCre-establishment; protocol error detection (AM only).

In the 3GPP NR system, the main services and functions of the MACsublayer include: mapping between logical channels and transportchannels; multiplexing/demultiplexing of MAC SDUs belonging to one ordifferent logical channels into/from transport blocks (TB) deliveredto/from the physical layer on transport channels; scheduling informationreporting; error correction through HARQ (one HARQ entity per cell incase of carrier aggregation (CA)); priority handling between UEs bymeans of dynamic scheduling; priority handling between logical channelsof one UE by means of logical channel prioritization; padding. A singleMAC entity may support multiple numerologies, transmission timings andcells. Mapping restrictions in logical channel prioritization controlwhich numerology(ies), cell(s), and transmission timing(s) a logicalchannel can use. Different kinds of data transfer services are offeredby MAC. To accommodate different kinds of data transfer services,multiple types of logical channels are defined i.e. each supportingtransfer of a particular type of information. Each logical channel typeis defined by what type of information is transferred. Logical channelsare classified into two groups: Control Channels and Traffic Channels.Control channels are used for the transfer of control plane informationonly, and traffic channels are used for the transfer of user planeinformation only. Broadcast Control Channel (BCCH) is a downlink logicalchannel for broadcasting system control information, paging ControlChannel (PCCH) is a downlink logical channel that transfers paginginformation, system information change notifications and indications ofongoing PWS broadcasts, Common Control Channel (CCCH) is a logicalchannel for transmitting control information between UEs and network andused for UEs having no RRC connection with the network, and DedicatedControl Channel (DCCH) is a point-to-point bi-directional logicalchannel that transmits dedicated control information between a UE andthe network and used by UEs having an RRC connection. Dedicated TrafficChannel (DTCH) is a point-to-point logical channel, dedicated to one UE,for the transfer of user information. A DTCH can exist in both uplinkand downlink. In Downlink, the following connections between logicalchannels and transport channels exist: BCCH can be mapped to BCH; BCCHcan be mapped to downlink shared channel (DL-SCH); PCCH can be mapped toPCH; CCCH can be mapped to DL-SCH; DCCH can be mapped to DL-SCH; andDTCH can be mapped to DL-SCH. In Uplink, the following connectionsbetween logical channels and transport channels exist: CCCH can bemapped to uplink shared channel (UL-SCH); DCCH can be mapped to UL-SCH;and DTCH can be mapped to UL-SCH.

FIG. 5 illustrates an example of a frame structure in the 3GPP basedwireless communication system.

The frame structure illustrated in FIG. 5 is purely exemplary and thenumber of subframes, the number of slots, and/or the number of symbolsin a frame may be variously changed. In the 3GPP based wirelesscommunication system, an OFDM numerology (e.g., subcarrier spacing(SCS), transmission time interval (TTI) duration) may be differentlyconfigured between a plurality of cells aggregated for one UE. Forexample, if a UE is configured with different SCSs for cells aggregatedfor the cell, an (absolute time) duration of a time resource (e.g. asubframe, a slot, or a TTI) including the same number of symbols may bedifferent among the aggregated cells. Herein, symbols may include OFDMsymbols (or CP-OFDM symbols), SC-FDMA symbols (or discrete Fouriertransform-spread-OFDM (DFT-s-OFDM) symbols).

Referring to FIG. 5, downlink and uplink transmissions are organizedinto frames. Each frame has T_(f)=10 ms duration. Each frame is dividedinto two half-frames, where each of the half-frames has 5 ms duration.Each half-frame consists of 5 subframes, where the duration T_(sf) persubframe is 1 ms. Each subframe is divided into slots and the number ofslots in a subframe depends on a subcarrier spacing. Each slot includes14 or 12 OFDM symbols based on a cyclic prefix (CP). In a normal CP,each slot includes 14 OFDM symbols and, in an extended CP, each slotincludes 12 OFDM symbols. The numerology is based on exponentiallyscalable subcarrier spacing Δf=2^(u)*15 kHz. The following table showsthe number of OFDM symbols per slot, the number of slots per frame, andthe number of slots per for the normal CP, according to the subcarrierspacing Δf=2^(u)*15 kHz.

TABLE 1 N^(slot) _(symb) N^(frame,u) _(slot) N^(subframe,u) _(slot) 0 1410 1 1 14 20 2 2 14 40 4 3 14 80 8 4 14 160 16

The following table shows the number of OFDM symbols per slot, thenumber of slots per frame, and the number of slots per for the extendedCP, according to the subcarrier spacing Δf=2^(u)*15 kHz.

TABLE 2 N^(slot) _(symb) N^(frame,u) _(slot) N^(subframe,u) _(slot) 2 1240 4

A slot includes plural symbols (e.g., 14 or 12 symbols) in the timedomain. For each numerology (e.g. subcarrier spacing) and carrier, aresource grid of N^(size,u) _(grid,x)*N^(RB) _(sc) subcarriers andN^(subframe,u) _(symb) OFDM symbols is defined, starting at commonresource block (CRB) N^(start,u) _(grid) indicated by higher-layersignaling (e.g. radio resource control (RRC) signaling), whereN^(size,u) _(grid,x) is the number of resource blocks (RBs) in theresource grid and the subscript x is DL for downlink and UL for uplink.N^(RB) _(sc) is the number of subcarriers per RB. In the 3GPP basedwireless communication system, N^(RB) _(sc) is 12 generally. There isone resource grid for a given antenna port p, subcarrier spacingconfiguration u, and transmission direction (DL or UL). The carrierbandwidth N^(size,u) _(grid) for subcarrier spacing configuration u isgiven by the higher-layer parameter (e.g. RRC parameter). Each elementin the resource grid for the antenna port p and the subcarrier spacingconfiguration u is referred to as a resource element (RE) and onecomplex symbol may be mapped to each RE. Each RE in the resource grid isuniquely identified by an index k in the frequency domain and an index lrepresenting a symbol location relative to a reference point in the timedomain. In the 3GPP based wireless communication system, an RB isdefined by 12 consecutive subcarriers in the frequency domain. In the3GPP NR system, RBs are classified into CRBs and physical resourceblocks (PRBs). CRBs are numbered from 0 and upwards in the frequencydomain for subcarrier spacing configuration u. The center of subcarrier0 of CRB 0 for subcarrier spacing configuration u coincides with ‘pointA’ which serves as a common reference point for resource block grids. Inthe 3GPP NR system, PRBs are defined within a bandwidth part (BWP) andnumbered from 0 to N^(size) _(BWP,i−1), where i is the number of thebandwidth part. The relation between the physical resource block n_(PRB)in the bandwidth part i and the common resource block n_(CRB) is asfollows: n_(PRB)=n_(CRB)+N^(size) _(BWP,i), where N^(size) _(BWP,i) isthe common resource block where bandwidth part starts relative to CRB 0.The BWP includes a plurality of consecutive RBs. A carrier may include amaximum of N (e.g., 5) BWPs. A UE may be configured with one or moreBWPs on a given component carrier. Only one BWP among BWPs configured tothe UE can active at a time. The active BWP defines the UE's operatingbandwidth within the cell's operating bandwidth.

FIG. 6 illustrates an example of a data flow in the 3GPP LTE system, andFIG. 7 illustrates an example of a data flow in the 3GPP NR system. InFIG. 6 and FIG. 7, “H” denotes headers and subheaders.

The MAC PDU is transmitted/received using radio resources through thePHY layer to/from an external device. The MAC PDU arrives to the PHYlayer in the form of a transport block. In the PHY layer, the uplinktransport channels UL-SCH and RACH are mapped to their physical channelsPUSCH and PRACH, respectively, and the downlink transport channelsDL-SCH, BCH and PCH are mapped to PDSCH, PBCH and PDSCH, respectively.In the PHY layer, uplink control information (UCI) is mapped to PUCCH,and downlink control information (DCI) is mapped to PDCCH. A MAC PDUrelated to UL-SCH is transmitted by a UE via a PUSCH based on an ULgrant, and a MAC PDU related to DL-SCH is transmitted by a BS via aPDSCH based on a DL assignment.

Functions of the RLC sublayer are performed by RLC entities. For an RLCentity configured at a BS, there is a peer RLC entity configured at theUE and vice versa. An RLC entity receives/delivers RLC SDUs from/toupper layer and sends/receives RLC PDUs to/from its peer RLC entity vialower layers. An RLC entity can be configured to perform data transferin one of the following three modes: Transparent Mode (TM),Unacknowledged Mode (UM) or Acknowledged Mode (AM). Consequently, an RLCentity is categorized as a TM RLC entity, an UM RLC entity or an AM RLCentity depending on the mode of data transfer that the RLC entity isconfigured to provide. A TM RLC entity is configured either as atransmitting TM RLC entity or a receiving TM RLC entity. Thetransmitting TM RLC entity receives RLC SDUs from upper layer and sendsRLC PDUs to its peer receiving TM RLC entity via lower layers. Thereceiving TM RLC entity delivers RLC SDUs to upper layer and receivesRLC PDUs from its peer transmitting TM RLC entity via lower layers. AnUM RLC entity is configured either as a transmitting UM RLC entity or areceiving UM RLC entity. The transmitting UM RLC entity receives RLCSDUs from upper layer and sends RLC PDUs to its peer receiving UM RLCentity via lower layers. The receiving UM RLC entity delivers RLC SDUsto upper layer and receives RLC PDUs from its peer transmitting UM RLCentity via lower layers. An AM RLC entity consists of a transmittingside and a receiving side. The transmitting side of an AM RLC entityreceives RLC SDUs from upper layer and sends RLC PDUs to its peer AM RLCentity via lower layers. The receiving side of an AM RLC entity deliversRLC SDUs to upper layer and receives RLC PDUs from its peer AM RLCentity via lower layers.

In the implementations of the present disclosure, the following servicesare expected by RLC from lower layer (i.e. MAC): data transfer; andnotification of a transmission opportunity together with the total sizeof the RLC PDU(s) to be transmitted in the transmission opportunity.

FIG. 8 illustrates a model of an acknowledged mode (AM) radio linkcontrol (RLC) entity in the 3GPP LTE system.

In the 3GPP LTE system, RLC SDUs of variable sizes which are bytealigned (i.e. multiple of 8 bits) are supported for all RLC entity type(TM, UM and AM RLC entity). RLC PDUs are formed only when a transmissionopportunity has been notified by lower layer (i.e. by MAC) and are thendelivered to lower layer. In the 3GPP LTE system, the main services andfunctions of the AM RLC entity include: transfer of upper layer PDUs;error correction through ARQ; concatenation, segmentation and reassemblyof RLC SDUs; re-segmentation of RLC data PDUs; and reordering of RLCdata PDUs.

Referring to FIG. 8, an AM RLC entity in the 3GPP LTE system(hereinafter, LTE AM RLC entity) can be configured to deliver/receiveRLC PDUs through the following logical channels: DL/UL DCCH or DL/ULDTCH. An LTE AM RLC entity delivers/receives the following RLC dataPDUs: acknowledge mode data (AMD) PDU, and AMD PDU segment. An LTE AMRLC entity delivers/receives the following RLC control PDU: STATUS PDU.When the transmitting side of an LTE AM RLC entity forms AMD PDUs fromRLC SDUs, it shall segment and/or concatenate the RLC SDUs so that theAMD PDUs fit within the total size of RLC PDU(s) indicated by lowerlayer at the particular transmission opportunity notified by lowerlayer. After the LTE AM RLC entity does the segmentation/concatenationprocess, it adds RLC headers to form the AMD PDUs.

The LTE AM RLC entity submits the AMD PDUs to lower layer (MAC). If theLTE AM RLC entity receives NACK for a transmitted RLC PDU or does notreceives any response for the transmitted RLC PDU with a poll, from apeer LTE AM RLC entity, for a certain period of time, the LTE AM RLCentity considers the RLC PDU stored in the transmission buffer forretransmission and stores the RLC PDU belonging to the transmissionwindow into the retransmission buffer. If the LTE AM RLC entity gets ACKfor the RLC PDU in the retransmission buffer, the LTE AM RLC entityupdates state variable and move the transmission window forward.

Alternatively, when submitting the AMD PDUs to lower layer (MAC), theLTE AM RLC entity could generate identical copies of each AMD PDU tosubmit one of the two copies to lower layer (MAC) and send the copy ofto the retransmission buffer. If the LTE AM RLC entity receives NACK fora transmitted RLC PDU or does not receives any response for thetransmitted RLC PDU with a poll, from a peer LTE AM RLC entity, for acertain period of time, the LTE AM RLC entity considers the RLC PDUstored in the retransmission buffer for retransmission. If the LTE AMRLC entity gets ACK for the transmitted RLC PDU in the retransmissionbuffer, the RLC PDU could be discarded.

The transmitting side of an LTE AM RLC entity supports retransmission ofRLC data PDUs (ARQ). The LTE AM RLC entity can re-segment the RLC dataPDU into AMD PDU segments if the RLC data PDU to be retransmitted doesnot fit within the total size of RLC PDU(s) indicated by lower layer atthe particular transmission opportunity notified by lower layer, wherethe number of re-segmentation is not limited. When the transmitting sideof an LTE AM RLC entity forms AMD PDUs from RLC SDUs received from upperlayer or AMD PDU segments from RLC data PDUs to be retransmitted, itshall include relevant RLC headers in the RLC data PDU.

In the 3GPP LTE system, the AM data is transferred between thetransmitting side of an LTE RLC entity and the receiving side of an LTERLC entity as follows. The transmitting side of an LTE AM RLC entityprioritizes transmission of RLC control PDUs over RLC data PDUs. Thetransmitting side of an LTE AM RLC entity prioritizes retransmission ofRLC data PDUs over transmission of new AMD PDUs. The transmitting sideof an LTE AM RLC entity shall maintain a transmitting window accordingto state variables VT(A) and VT(MS) as follows:

a SN falls within the transmitting window if VT(A)⇐SN<VT(MS);

a SN falls outside of the transmitting window otherwise.

The transmitting entity of each LTE AM RLC entity shall maintain VT(A)and VT(MS). VT(A) is an acknowledgement state variable which holds thevalue of the SN of the next AMD PDU for which a positive acknowledgmentis to be received in-sequence, and it serves as the lower edge of thetransmitting window. VT(A) is initially set to 0, and is updatedwhenever the LTE AM RLC entity receives a positive acknowledgment for anAMD PDU with SN=VT(A). VT(MS) is the maximum send state variable whichequals to VT(A)+AM_Window_Size, and it serves as the higher edge of thetransmitting window. AM_Window_Size is a constant used by both thetransmitting side and the receiving side of each LTE AM RLC entity tocalculate VT(MS) from VT(A), and VR(MR) from VR(R). AM_Window_Size=512when a 10 bit SN is used, AM_Window_Size=32768 when a 16 bit SN is used.The receiving entity of each LTE AM RLC entity shall maintain VR(R) andVR(MR). VR(R) is a receive state variable which holds the value of theSN following the last in-sequence completely received AMD PDU, and itserves as the lower edge of the receiving window. VR(R) is initially setto 0, and is updated whenever the AM RLC entity receives an AMD PDU withSN=VR(R). VR(MR) is the maximum acceptable receive state variable whichequals to VR(R)+AM_Window_Size, and it holds the value of the SN of thefirst AMD PDU that is beyond the receiving window and serves as thehigher edge of the receiving window.

The transmitting side of an LTE AM RLC entity shall not deliver to lowerlayer any RLC data PDU whose SN falls outside of the transmittingwindow. When delivering a new AMD PDU to lower layer, the transmittingside of an AM RLC entity shall set the SN of the AMD PDU to VT(S), andthen increment VT(S) by one. The transmitting side of each LTE AM RLCentity shall maintain VT(S). VT(S) is a send state variable which holdsthe value of the SN to be assigned for the next newly generated AMD PDU.VT(S) is initially set to 0, and is updated whenever the AM RLC entitydelivers an AMD PDU with SN=VT(S).

The transmitting side of an LTE AM RLC entity can receive a positiveacknowledgement (confirmation of successful reception by its peer AM RLCentity) for a RLC data PDU by a STATUS PDU from its peer LTE AM RLCentity. When receiving a positive acknowledgement for an AMD PDU withSN=VT(A), the transmitting side of an LTE AM RLC entity shall:

set VT(A) equal to the SN of the AMD PDU with the smallest SN, whose SNfalls within the range VT(A)<=SN<=VT(S) and for which a positiveacknowledgment has not been received yet.

if positive acknowledgements have been received for all AMD PDUsassociated with a transmitted RLC SDU, send an indication to the upperlayers of successful delivery of the RLC SDU.

The transmitting side of an LTE AM RLC entity can receive a negativeacknowledgement (notification of reception failure by its peer LTE AMRLC entity) for an AMD PDU or a portion of an AMD PDU by a STATUS PDUfrom its peer LTE AM RLC entity. When receiving a negativeacknowledgement for an AMD PDU or a portion of an AMD PDU by a STATUSPDU from its peer LTE AM RLC entity, the transmitting side of the LTE AMRLC entity shall:

if the SN of the corresponding AMD PDU falls within the rangeVT(A)<=SN<VT(S), consider the AMD PDU or the portion of the AMD PDU forwhich a negative acknowledgement was received for retransmission.

When an AMD PDU or a portion of an AMD PDU is considered forretransmission, the transmitting side of the LTE AM RLC entity shall:

if the AMD PDU is considered for retransmission for the first time, setthe RETX_COUNT associated with the AMD PDU to zero;

else, if it (the AMD PDU or the portion of the AMD PDU that isconsidered for retransmission) is not pending for retransmissionalready, or a portion of it is not pending for retransmission already,increment the RETX_COUNT;

if RETX_COUNT=maxRetxThreshold, indicate to upper layers that maxretransmission has been reached. RETX_COUNT is a counter maintained bythe transmitting side of each LTE AM RLC entity. RETX_COUNT is initiallyset to 0 and counts the number of AMD PDUs sent since the most recentpoll bit was transmitted. maxRetxThreshold is a parameter configured byRRC and used by the transmitting side of each LTE AM RLC entity to limitthe number of retransmissions of an AMD PDU. If the transmitting side ofan LTE AM RLC entity is a UE, the UE is configured with maxRetxThresholdby receiving maxRetxThreshold via RRC signaling from a network (e.g.BS).

When retransmitting an AMD PDU, the transmitting side of an LTE AM RLCentity shall:

if the AMD PDU can entirely fit within the total size of RLC PDU(s)indicated by lower layer at the particular transmission opportunity,deliver the AMD PDU as it is except for the P field to lower layer;

otherwise, segment the AMD PDU, form a new AMD PDU segment which willfit within the total size of RLC PDU(s) indicated by lower layer at theparticular transmission opportunity and deliver the new AMD PDU segmentto lower layer.

When retransmitting a portion of an AMD PDU, the transmitting side of anLTE AM RLC entity shall segment the portion of the AMD PDU as necessary,form a new AMD PDU segment which will fit within the total size of RLCPDU(s) indicated by lower layer at the particular transmissionopportunity and deliver the new AMD PDU segment to lower layer.

When forming a new AMD PDU segment, the transmitting side of an AM RLCentity shall only map the Data field of the original AMD PDU to the Datafield of the new AMD PDU segment, set the header of the new AMD PDUsegment; and set the P field as the polling procedure described below.

An AMD PDU consists of a Data field and an AMD PDU header. The AMD PDUheader includes a P field and an SN field. In the 3GPP LTE system, theSN field indicates an SN of the corresponding AMD PDU. For an AMD PDUsegment, the SN field indicates the SN of the original AMD PDU fromwhich the AMD PDU segment was constructed from. The P field indicateswhether or not the transmitting side of an LTE AM RLC entity requests aSTATUS report from its peer LTE AM RLC entity. In the 3GPP LTE and NRsystems, the interpretation of the P field is provided in the followingtable.

TABLE 3 Value Description 0 Status report not requested 1 Status reportis requested

An LTE AM RLC entity can poll its peer AM RLC entity in order to triggerSTATUS reporting at the peer LTE AM RLC entity. Upon assembly of a newAMD PDU, the transmitting side of an LTE AM RLC entity shall:>incrementPDU_WITHOUT_POLL by one;

increment BYTE_WITHOUT_POLL by every new byte of Data field element thatit maps to the Data field of the RLC data PDU;

if PDU_WITHOUT_POLL>=pollPDU; or

if BYTE_WITHOUT_POLL>=pollByte;

include a poll in the RLC data PDU as described below.

Upon assembly of an AMD PDU or AMD PDU segment, the transmitting side ofan AM RLC entity shall:

if both the transmission buffer and the retransmission buffer becomesempty (excluding transmitted RLC data PDU awaiting for acknowledgements)after the transmission of the RLC data PDU; or

if no new RLC data PDU can be transmitted after the transmission of theRLC data PDU (e.g. due to window stalling);

include a poll in the RLC data PDU as described below.

The transmitting side of each LTE AM RLC entity shall maintainPDU_WITHOUT_POLL and BYTE_WITHOUT_POLL. PDU_WITHOUT_POLL is a counterwhich is initially set to 0 and counts the number of AMD PDUs sent sincethe most recent poll bit was transmitted. BYTE_WITHOUT_POLL is a counterwhich is initially set to 0 and counts the number of data bytes sentsince the most recent poll bit was transmitted. pollPDU and pollByte areparameters configured by RRC. pollPDU is a parameter used by thetransmitting side of each LTE AM RLC entity to trigger a poll for everypollPDU PDUs, and pollByte is a parameter used by the transmitting sideof each LTE AM RLC entity to trigger a poll for every pollByte bytes. Ifthe transmitting side of an LTE AM RLC entity is a UE, the UE isconfigured with pollPDU and pollByte by receiving pollPDU and pollBytevia RRC signaling from a network (e.g. BS).

To include a poll in a RLC data PDU, the transmitting side of an LTE AMRLC entity shall set the P field of the RLC data PDU to “1”; setPDU_WITHOUT_POLL to 0; set BYTE_WITHOUT_POLL to 0. After delivering aRLC data PDU including a poll to lower layer and after incrementing ofVT(S) if necessary, the transmitting side of an AM RLC entity shall:

set POLL_SN to VT(S)−1;

if t-PollRetransmit is not running:

start t-PollRetransmit;

else:

restart t-PollRetransmit.

The transmitting side of each LTE AM RLC entity shall maintain POLL_SN.POLL_SN is the poll send state variable which holds the value of VT(S)−1upon the most recent transmission of a RLC data PDU with the poll bitset to “1”. POLL_SN is initially set to 0. t-PollRetransmit is a timerconfigured by RRC and used by the transmitting side of each LTE AM RLCentity to retransmit a poll. If the transmitting side of an LTE AM RLCentity is a UE, the UE is configured with t-PollRetransmit by receivingt-PollRetransmit via RRC signaling from a network (e.g. BS). Uponreception of a STATUS report from the receiving RLC AM entity thetransmitting side of an LTE AM RLC entity shall:

if the STATUS report comprises a positive or negative acknowledgementfor the RLC data PDU with sequence number equal to POLL_SN:

if t-PollRetransmit is running:

stop and reset t-PollRetransmit.

Upon expiry of t-PollRetransmit, the transmitting side of an AM RLCentity shall:

if both the transmission buffer and the retransmission buffer are empty(excluding transmitted RLC data PDU awaiting for acknowledgements); or

if no new RLC data PDU can be transmitted (e.g. due to window stalling):

consider the AMD PDU with SN=VT(S)−1 for retransmission; or

consider any AMD PDU which has not been positively acknowledged forretransmission;

include a poll in a RLC data PDU as described above.

An LTE AM RLC entity sends STATUS PDUs to its peer LTE AM RLC entity inorder to provide positive and/or negative acknowledgements of RLC PDUs(or portions of them). Triggers to initiate STATUS reporting in an LTEAM RLC entity include polling from its peer LTE AM RLC entity.

As described above, in the 3GPP LTE system, a new AM Data PDU (AMD PDU)can be constructed only when notification of a transmission opportunityis received from lower layer (MAC). When there is notification of atransmission opportunity, a single AMD PDU is constructed and submittedto MAC. The sequence number (SN) of the newly constructed AMD PDU is setto VT(S) which is a send state variable that holds the value of the SNto be assigned for the next newly generated AMD PDU. In the 3GPP LTEsystem, VT(S)−1 means SN of the last constructed AMD PDU at thetransmitting side of an AM RLC entity. In this condition, when a pollretransmission timer (t-PollRetransmit) expires, the transmitting sideof an AM RLC entity can consider the AMD PDU with SN=VT(S)−1, whichmeans SN of the last constructed AMD PDU, for retransmission.

In the 3GPP NR system, RLC SDUs of variable sizes which are byte aligned(i.e. multiple of 8 bits) are supported for all RLC entity type (TM, UMand AM RLC entity), which is similar in the 3GPP LTE system. In the 3GPPNR system, however, each RLC SDU is used to construct an RLC PDU withoutwaiting for notification of a transmission opportunity from the lowerlayer (i.e., by MAC). In the case of UM and AM RLC entities, as shown inFIG. 7, an RLC SDU may be segmented and transported using two or moreRLC PDUs based on the notification(s) from the lower layer. RLC PDUs aresubmitted to lower layer only when a transmission opportunity has beennotified by lower layer (i.e. by MAC). In other words, in the 3GPP NRsystem, the RLC entity is allowed to construct RLC data PDUs in advanceeven without notification of a transmission opportunity from the lowerlayer, i.e., pre-construction of RLC data PDU is allowed. When and howmany RLC data PDUs are pre-constructed is left up to UE implementation.Therefore, a send state variable (hereinafter, TX_Next) which holds thevalue of the SN to be assigned for the next newly generated AMD PDU canbe incremented whenever a new AMD PDU is constructed withoutnotification of a transmission opportunity by the lower layer. In thiscondition, if the RLC SDU with SN=TX_Next−1 is considered forretransmission upon expiry of t-PollRetransmit as in the 3GPP LTEsystem, the transmitting side of an AM RLC entity would try toretransmit the last pre-constructed AMD PDU which is not transmitted yetand not on the transmitting window. This means that the transmittingside of an AM RLC entity may select a wrong RLC SDU for retransmission,which is out of the transmitting window. If no new RLC SDU can betransmitted (e.g. due to window stalling), the transmitting side of anAM RLC entity cannot retransmit an RLC SDU because the selected RLC SDUis not on the transmitting window and there is no space on thetransmitting window to transmit the AMD PDU which contains the selectedRLC SDU. In other words, the window stalling cannot be resolved.Therefore, in NR, the RLC SDU with SN=TX_Next−1 should not be consideredfor retransmission and new RLC SDU selection rule for retransmissionshould be introduced to resolve the problem.

In an implementation of the present disclosure, when a pollretransmission timer (t-PollRetransmit) expires, if both thetransmission buffer and the retransmission buffer are empty (excludingtransmitted RLC SDU or RLC SDU segment awaiting acknowledgements) or ifno new RLC SDU can be transmitted (e.g. due to window stalling), thetransmitting side of an AM RLC entity considers the RLC SDU with thehighest SN among the RLC SDUs submitted to lower layer (i.e., MAC) forretransmission. In other words, the RLC SDU with the highest SN amongthe RLC SDUs transmitted by a transmitting device to a receiving deviceis considered for retransmission. In this implementation, the RLC SDUwith the highest SN among the RLC SDUs submitted to lower layer may beor may not be a RLC SDU submitted with a poll.

Alternatively, in another implementation of the present disclosure, whena poll retransmission timer (t-PollRetransmit) expires, if both thetransmission buffer and the retransmission buffer are empty (excludingtransmitted RLC SDU or RLC SDU segment awaiting acknowledgements) or ifno new RLC SDU can be transmitted (e.g. due to window stalling), thetransmitting side of an AM RLC entity considers the RLC SDU, whichcorresponds to the highest SN of the AMD PDU including a poll among theset of AMD PDUs including a poll submitted to lower layer (i.e., MAC),for retransmission.

The implementation(s) of the present disclosure can be applied to anytype of UE, e.g., a machine type communication (MTC) UE, narrow bandinternet of things (NB-IoT) UE, normal UE.

A poll retransmission timer, which is t-PollRetransmit, is used by thetransmitting side of an AM RLC entity in order to retransmit a poll.t-PollRetransmit is configured by RRC. If the transmitting side of theAM RLC entity is a UE, the UE is configured with t-PollRetransmit byreceiving t-PollRetransmit via RRC signaling from a network (e.g. BS).

In the present disclosure, the transmitted RLC SDUs or RLC SDU segmentsawaiting acknowledgements means that the transmitting side of an AM RLCentity already transmits RLC SDUs and RLC SDU segments and waits theSTATUS report for the transmitted RLC SDUs and RLC SDU segments.

In the present disclosure, “window stalling” means stopping atransmitting window of RLC or means pausing to make the transmittingwindow progress. For example, if the transmitting window becomes fullthen the RLC entity may not transmit any new RLC PDU until the loweredge of the transmitting window is advanced. This situation may bereferred to as window stalling. In other words, window stalling meansthat the transmitting side of an AM RLC entity transmits all RLC SDUsand RLC SDU segments within the transmitting window but not yet receivedany acknowledgements for the transmitted RLC SDUs and RLC SDU segments.Thus, the transmitting side of an AM RLC entity cannot transmit a newRLC SDU because the transmitting side of an AM RLC entity should notsubmit an AMD PDU, which contains an RLC SDU with SN falls outside ofthe transmitting window, to lower layer.

In the present disclosure, the highest SN is the highest SN based onmodulus operation. For example, when SN can be assigned from 0 to 1023,if the currently assigned SNs start from 1000 and end to 1, the highestSN is 1 because modulus operation sets 1024 and 1025 to 0 and 1respectively. However if the currently assigned SNs start from 1 and endto 500, the highest SN is 500.

In the present disclosure, an AMD PDU including a poll means an AMD PDUwith the poll bit set to “1”. In other words, in the present disclosure,including a poll in an RLC PDU refers to including the value “1” in theP field included in the RLC PDU, and an RLC PDU including a poll meansan RLC PDU whose P field includes the value “1”.

In the implementation(s) of the present disclosure, the transmittingside of an AM RLC entity is configured with timers and parameters forpolling procedure by receiving polling configuration information from anetwork including the followings:

t-PollRetransmit in order to retransmit a poll after expiry oft-PollRetransmit.

pollPDU to trigger a poll for every pollPDU PDUs;

pollByte to trigger a poll for every pollByte bytes. pollPDU is aparameter used by by the transmitting side of each AM RLC entity totrigger a poll for every pollPDU PDUs, and pollByte is a parameter usedby the transmitting side of each AM RLC entity to trigger a poll forevery pollByte bytes.

In the implementation(s) of the present disclosure, the transmittingside of an AM RLC entity manages the following counters:

PDU_WITHOUT_POLL counts the number of AMD PDUs sent since the mostrecent poll bit was transmitted, and this counter is initially set to 0;

BYTE_WITHOUT_POLL counts the number of data bytes sent since the mostrecent poll bit was transmitted, and this counter is initially set to 0.

In the implementation(s) of the present disclosure, when thetransmitting side of an AM RLC entity submits a set of AMD PDUs afternotification of a transmission opportunity by lower layer (i.e., MAC),the transmitting side of the AM RLC entity may submit an AMD PDUsequentially in increasing order of SN to lower layer (i.e., MAC).Alternatively, the transmitting side of the AM RLC entity may submitmultiple AMD PDUs to a lower layer simultaneously.

In the present disclosure, all state variables and all counters arenon-negative integers.

FIG. 9 illustrates a model of AM RLC entity which can be used in theimplementation(s) of the present disclosure.

Referring to FIG. 9, an AM RLC entity can be configured todeliver/receive RLC PDUs through the following logical channels: DL/ULDCCH or DL/UL DTCH. An AM RLC entity delivers/receives the following RLCdata PDUs: AMD PDU. An AMD PDU contains either one complete RLC SDU orone RLC SDU segment. An AM RLC entity delivers/receives a STATUS PDUwhich is an RLC control PDU.

In the implementation(s) of the present disclosure, the transmittingside of an AM RLC entity generates AMD PDU(s) for each RLC SDU. Whennotified of a transmission opportunity by the lower layer, thetransmitting AM RLC entity segments the RLC SDUs, if needed, so that thecorresponding AMD PDUs, with RLC headers updated as needed, fit withinthe total size of RLC PDU(s) indicated by lower layer. The transmittingside of an AM RLC entity supports retransmission of RLC SDUs or RLC SDUsegments (ARQ). If the RLC SDU or RLC SDU segment to be retransmitted(including the RLC header) does not fit within the total size of RLCPDU(s) indicated by lower layer at the particular transmissionopportunity notified by lower layer, the AM RLC entity can segment theRLC SDU or re-segment the RLC SDU segments into RLC SDU segments, wherethe number of re-segmentation is not limited. When the transmitting sideof an AM RLC entity forms AMD PDUs from RLC SDUs or RLC SDU segments, itincludes relevant RLC headers in the AMD PDU.

In the implementation(s) of the present disclosure, an AMD PDU consistsof a Data field and an AMD PDU header. An AM RLC entity may configuredby RRC to use either a 12 bit SN or a 18 bit SN. An AMD PDU headercontains a P field and a SN field. The SN field indicates the SN of thecorresponding RLC SDU. For RLC AM, the SN is incremented by one forevery RLC SDU.

In the implementation(s) of the present disclosure, data transferprocedures between the transmitting side of an RLC entity and thereceiving side of an RLC entity are as follows.

The transmitting side of an AM RLC entity prioritizes transmission ofRLC control PDUs over AMD PDUs. The transmitting side of an AM RLCentity prioritizes transmission of AMD PDUs containing previouslytransmitted RLC SDUs or RLC SDU segments over transmission of AMD PDUscontaining not previously transmitted RLC SDUs or RLC SDU segments.

The transmitting side of an AM RLC entity shall maintain a transmittingwindow according to the state variable TX_Next_Ack as follows:

a SN falls within the transmitting window ifTX_Next_Ack<=SN<TX_Next_Ack+AM_Window_Size;

a SN falls outside of the transmitting window otherwise. TX_Next_Ack isthe acknowledgement state variable maintained in the transmitting sideof each AM RLC entity, and holds the value of the SN of the next RLC SDUfor which a positive acknowledgment is to be received in-sequence, andit serves as the lower edge of the transmitting window. It is initiallyset to 0, and is updated whenever the AM RLC entity receives a positiveacknowledgment for an RLC SDU with SN=TX_Next_Ack. AM_Window_Size is aconstant used by both the transmitting side and the receiving side ofeach AM RLC entity. AM_Window_Size=2048 when a 12 bit SN is used,AM_Window_Size=131072 when an 18 bit SN is used.

The transmitting side of an AM RLC entity does not submit to lower layerany AMD PDU whose SN falls outside of the transmitting window. For eachRLC SDU received from the upper layer (e.g. PDCP), the AM RLC entityassociates a SN with the RLC SDU equal to TX_Next and constructs an AMDPDU by setting the SN of the AMD PDU to TX_Next, and increments TX_Nextby one. TX_Next is a state variable maintained in the transmitting sideof each AM RLC entity and holds the value of the SN to be assigned forthe next newly generated AMD PDU. TX_Next is initially set to 0, and isupdated whenever the AM RLC entity constructs an AMD PDU with SN=TX_Nextwhich contains an RLC SDU or the last segment of an RLC SDU. In otherwords, TX_Next would be updated whenever the AM RLC entity constructs anAMD PDU containing an RLC SDU with TX_Next or the last segment of an RLCSDU with SN=TX_Next, since the SN field in an AMD PDU indicates the SNof the corresponding RLC PDU.

When submitting an AMD PDU that contains a segment of an RLC SDU, tolower layer, the transmitting side of an AM RLC entity sets the SN ofthe AMD PDU to the SN of the corresponding RLC SDU.

The transmitting side of an AM RLC entity can receive a positiveacknowledgement (confirmation of successful reception by its peer AM RLCentity) for an RLC SDU by a STATUS PDU from its peer AM RLC entity. Whenreceiving a positive acknowledgement for an RLC SDU with SN=x, thetransmitting side of an AM RLC entity sends an indication to the upperlayers of successful delivery of the RLC SDU; and sets TX_Next_Ack equalto the SN of the RLC SDU with the smallest SN, whose SN falls within therange TX_Next_Ack<=SN<=TX_Next and for which a positive acknowledgmentshas not been received yet. In other words, when receiving a positiveacknowledgement for an RLC SDU with SN=x, the transmitting side of an AMRLC entity moves the lower edge of the transmitting window forward tothe smallest SN of the RLC SDU for which a positive acknowledgment hasnot been received within the transmitting window.

The transmitting side of an AM RLC entity can receive a negativeacknowledgement (notification of reception failure by its peer AM RLCentity) for an RLC SDU or an RLC SDU segment by a STATUS PDU from itspeer AM RLC entity. When receiving a negative acknowledgement for an RLCSDU or an RLC SDU segment by a STATUS PDU from its peer AM RLC entity,the transmitting side of the AM RLC entity may consider the RLC SDU orthe RLC SDU segment, for which a negative acknowledgement was received,for retransmission if the SN of the corresponding RLC SDU falls withinthe range TX_Next_Ack<=SN<TX_Next.

When an RLC SDU or an RLC SDU segment is considered for retransmission,the transmitting side of the AM RLC entity:

sets the RETX_COUNT associated with the RLC SDU to zero if the RLC SDUor RLC SDU segment is considered for retransmission for the first time;

increments the RETX_COUNT if it (the RLC SDU or the RLC SDU segment thatis considered for retransmission) is not pending for retransmissionalready and the RETX_COUNT associated with the RLC SDU has not beenincremented due to another negative acknowledgment in the same STATUSPDU;

indicate to upper layers that max retransmission has been reached ifRETX_COUNT=maxRetxThreshold. RETX_COUNT is a counter maintained in thetransmitting side of each AM RLC entity and counts the number ofretransmissions of an RLC SDU or RLC SDU segment. There is oneRETX_COUNT counter maintained per RLC SDU. maxRetxThreshold is aparameter configured by RRC, and used by the transmitting side of eachAM RLC entity to limit the number of retransmissions corresponding to anRLC SDU, including its segments. If the transmitting side of an AM RLCentity is a UE, the UE is configured with maxRetxThreshold by receivingmaxRetxThreshold via RRC signaling from a network (e.g. BS).

When retransmitting an RLC SDU or an RLC SDU segment, the transmittingside of an AM RLC entity:

segments the RLC SDU or the RLC SDU segment if needed;

forms a new AMD PDU which will fit within the total size of AMD PDU(s)indicated by lower layer at the particular transmission opportunity; and

submits the new AMD PDU to lower layer.

When forming a new AMD PDU, the transmitting side of an AM RLC entity:

maps only the original RLC SDU or RLC SDU segment to the Data field ofthe new AMD PDU; and

modifies the header of the new AMD PDU. Modifying the header of the newAMD PDU comprises setting the P field as described below.

Upon notification of transmission opportunity by lower layer (i.e.,MAC), for each AMD PDU submitted for transmission such that the AMD PDUcontains either a not previously transmitted RLC SDU or an RLC SDUsegment containing not previously transmitted byte segment, thetransmitting side of an AM RLC entity:

increments PDU_WITHOUT_POLL by one;

increments BYTE_WITHOUT_POLL by every new byte of Data field elementthat it maps to the Data field of the AMD PDU;

if PDU_WITHOUT_POLL>=pollPDU; or

if BYTE_WITHOUT_POLL>=pollByte;

sets the P field of the AMD PDU to “1”;

sets PDU_WITHOUT_POLL to 0;

sets BYTE_WITHOUT_POLL to 0;

submits the AMD PDU to lower layer.

Upon notification of a transmission opportunity by lower layer, for eachAMD PDU submitted for transmission, the transmitting side of an AM RLCentity:

if both the transmission buffer and the retransmission buffer becomesempty (excluding transmitted RLC SDUs or RLC SDU segments awaitingacknowledgements) after the transmission of the AMD PDU; or

if no new RLC SDU can be transmitted after the transmission of the AMDPDU (e.g. due to window stalling);

sets the P field of the AMD PDU to “1”;

sets PDU_WITHOUT_POLL to 0;

sets BYTE_WITHOUT_POLL to 0;

submits the AMD PDU to lower layer.

It is required that empty RLC buffer (excluding transmitted RLC SDUs orRLC SDU segments awaiting acknowledgments) not lead to unnecessarypolling when data waits in the upper layer (e.g. PDCP, SDAP, RRC). Inorder to keep the empty RLC buffer (excluding transmitted RLC SDUs orRLC SDU segments awaiting acknowledgments) from leading to unnecessarypolling, the transmitting side of a an AM RLC entity may set the P fieldof an AMD PDU to “0” even when the RLC buffer becomes empty aftertransmission of the AMD PDU.

When the transmitting side of an AM RLC entity submits an AMD PDU tolower layer, the transmitting side of an AM RLC entity:

sets POLL_SN to SN of the AMD PDU including a poll, if the AMD PDUincluding a poll is submitted to lower layer;

starts t-PollRetransmit, if t-PollRetransmit is not running;

restarts t-PollRetransmit, if t-PollRetransmit is running.

When a poll retransmission timer t-PollRetransmit expires, thetransmitting side of an AM RLC entity performs transmission orretransmission procedure to retransmit a poll.

When t-PollRetransmit expires, the transmitting side of an AM RLCentity:

if both the transmission buffer and the retransmission buffer are empty(excluding transmitted RLC SDU or RLC SDU segment awaitingacknowledgements); and/or

if no new RLC SDU or RLC SDU segment can be transmitted (e.g. due towindow stalling):

considers the RLC SDU with the highest SN among the RLC SDUs submittedto lower layer for retransmission;

includes a poll in an AMD PDU as described above.

In particular, the implementation of the present disclosure, upon expiryof t-PollRetransmit, when the RLC buffer is empty (excluding transmittedRLC SDU or RLC SDU segment awaiting acknowledgements) and/or when no newRLC SDU or RLC SDU segment can be transmitted (e.g. due to windowstalling), the transmitting side of an AM RLC entity considers the RLCSDU with the highest SN among the RLC SDUs submitted to MAC forretransmission. The transmitting side of an AM RLC entity includes apoll in an AMD PDU including the RLC SDU considered for retransmission,and submits the AMD PDU to MAC for transmission when there is atransmission opportunity. In the implementation of the presentdisclosure, the RLC SDU considered for retransmission upon expiry oft-PollRetransmit, and when the RLC buffer is empty (excludingtransmitted RLC SDU or RLC SDU segment awaiting acknowledgements), or nonew RLC SDU or RLC SDU segment can be transmitted (e.g. due to windowstalling) may be or may be not an RLC SDU having been submitted with apoll to MAC. In the implementation of the present disclosure, the RLCSDU considered for retransmission upon expiry of t-PollRetransmit, andwhen no new RLC SDU or RLC SDU segment can be transmitted (e.g. due towindow stalling) may be not an RLC SDU included in the last constructedAMD PDU. This implementation of the present disclosure is advantageousin that the transmitting side of an AM RLC entity requests that thereceiving side of the AM RLC entity send a status report on up to thelast RLC SDU actually sent by the transmitting side of the AM RLC entityto the receiving side of the AM RLC entity.

When the transmitting side of an AM RLC entity receives a STATUS reportcomprising a positive or negative acknowledgement for the RLC SDU withSN equal to POLL_SN, the transmitting side of an AM RLC entity stops andresets t-PollRetransmit, if t-PollRetransmit is running.

FIGS. 10A and 10B illustrate examples of data transfer according to theimplementation(s) of the present disclosure. In FIGS. 10A and 10B, it isassumed that all RLC SDUs have same size which is 100 bytes, pollPDU is3, pollByte is 400 bytes, and the transmitting window size is 8.

FIG. 10A shows an example where t-PollRetransmit expires and both thetransmission buffer and the retransmission buffer are empty (excludingtransmitted RLC SDU or RLC SDU segment awaiting acknowledgements). InFIG. 10A, when the transmitting side of an AM RLC entity receivesnotification of transmission opportunity by lower layer (e.g. MAC), thetransmitting side of the AM RLC entity:

for AMD PDU which contains the RLC SDU for SN4: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; andsubmits the AMD PDU, which contains the RLC SDU for SN4, to lower layer;

for AMD PDU which contains the RLC SDU for SN5: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; andsubmits the AMD PDU, which contains the RLC SDU for SN5, to lower layer;

for AMD PDU which contains the RLC SDU for SN6: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; setsthe P field of the AMD PDU to “1” which contains the RLC SDU for SN6because PDU_WITHOUT_POLL is equal to pollPDU=3; sets PDU_WITHOUT_POLL to0; sets BYTE_WITHOUT_POLL to 0; and submits the AMD PDU, which containsthe RLC SDU for SN6, to lower layer; sets POLL_SN to SN6; startst-PollRetransmit; increments PDU_WITHOUT_POLL by one;

for AMD PDU which contains the RLC SDU for SN7: incrementsBYTE_WITHOUT_POLL by 100 bytes; submits the AMD PDU, which contains theRLC SDU for SN7, to lower layer; increments PDU_WITHOUT_POLL by one;

for AMD PDU which contains the RLC SDU for SN8: incrementsBYTE_WITHOUT_POLL by 100 bytes; sets the P field of the AMD PDU to “1”which contains the RLC SDU for SN8 because both the transmission bufferand the retransmission buffer are empty (excluding transmitted RLC SDUor RLC SDU segment awaiting acknowledgements) after the transmission ofthe AMD PDU; sets PDU_WITHOUT_POLL to 0; sets BYTE_WITHOUT_POLL to 0;submits the AMD PDU, which contains the RLC SDU for SN8, to lower layer;sets POLL_SN to SN8; and restarts t-PollRetransmit.

All RLC SDUs from SN4 to SN8 are transmitted and wait foracknowledgement. As shown in FIG. 10A, when the t-PollRetransmitexpires, the transmitting side of an AM RLC entity:

checks whether the transmission buffer and the retransmission buffer areempty or not;

considers the RLC SDU with SN8 for retransmission because SN8 is thehighest SN among the RLC SDUs submitted to lower layer (i.e., MAC), ifthe transmission buffer and the retransmission buffer are empty;

retransmits the selected RLC SDU with SN8.

FIG. 10B shows an example where t-PollRetransmit expires and no new RLCSDU can be transmitted (e.g. due to window stalling). In FIG. 10B, whenthe transmitting side of an AM RLC entity receives notification of atransmission opportunity by lower layer (e.g. MAC), the transmittingside of the AM RLC entity:

for AMD PDU which contains the RLC SDU for SN1: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; andsubmits the AMD PDU, which contains the RLC SDU for SN1, to lower layer;

for AMD PDU which contains the RLC SDU for SN2: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; andsubmits the AMD PDU, which contains the RLC SDU for SN2, to lower layer;

for AMD PDU which contains the RLC SDU for SN3: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; setsthe P field of the AMD PDU to “1” which contains the RLC SDU for SN3because PDU_WITHOUT_POLL is equal to pollPDU=3; sets PDU_WITHOUT_POLL to0; sets BYTE_WITHOUT_POLL to 0; submits the AMD PDU, which contains theRLC SDU for SN3, to lower layer; sets POLL_SN to SN3; and startst-PollRetransmit;

for AMD PDU which contains the RLC SDU for SN4: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; andsubmits the AMD PDU, which contains the RLC SDU for SN4, to lower layer;

for AMD PDU which contains the RLC SDU for SN5: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; andsubmits the AMD PDU, which contains the RLC SDU for SN5, to lower layer;

for AMD PDU which contains the RLC SDU for SN6: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; setsthe P field of the AMD PDU to “1” which contains the RLC SDU for SN6because PDU_WITHOUT_POLL is equal to pollPDU=3; sets PDU_WITHOUT_POLL to0; sets BYTE_WITHOUT_POLL to 0; submits the AMD PDU, which contains theRLC SDU for SN6, to lower layer; and sets POLL_SN to SN6; and restartst-PollRetransmit;

for AMD PDU which contains the RLC SDU for SN7: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; andsubmits the AMD PDU, which contains the RLC SDU for SN7, to lower layer;

for AMD PDU which contains the RLC SDU for SN8: incrementsPDU_WITHOUT_POLL by one; increments BYTE_WITHOUT_POLL by 100 bytes; setsthe P field of the AMD PDU to “1” which contains the RLC SDU for SN8because no new RLC SDU can be transmitted after the transmission of theAMD PDU (e.g. due to window stalling); sets PDU_WITHOUT_POLL to 0; setsBYTE_WITHOUT_POLL to 0; submits the AMD PDU, which contains the RLC SDUfor SN8, to lower layer; sets POLL_SN to SN8; and restartst-PollRetransmit.

All RLC SDUs from SN1 to SN8 are transmitted and wait foracknowledgement. As shown in FIG. 10B, when the t-PollRetransmitexpires, the transmitting side of an AM RLC entity:

checks whether no new RLC SDU can be transmitted (e.g. due to windowstalling);

considers the RLC SDU with SN8 for retransmission because SN8 is thehighest SN among the RLC SDUs submitted to lower layer (i.e., MAC), ifno new RLC SDU can be transmitted (e.g. due to window stalling);

retransmits the selected RLC SDU with SN8.

In FIG. 10A and FIG. 10B, when the t-PollRetransmit expires, if both thetransmission buffer and the retransmission buffer are empty (excludingtransmitted RLC SDU or RLC SDU segment awaiting acknowledgements) or ifno new RLC SDU can be transmitted (e.g. due to window stalling), thetransmitting side of an AM RLC entity can consider the RLC SDU with SN8for retransmission because SN8 is the highest SN of the AMD PDU amongthe set of AMD PDUs submitted to lower layer (i.e., MAC) fortransmission.

FIG. 11 is a block diagram illustrating examples of communicationdevices which can perform method(s) of the present disclosure.

In FIG. 11, one of the communication device 1100 and the communicationdevice 1200 may be a user equipment (UE) and the other one mat be a basestation (BS). Alternatively, one of the communication device 1100 andthe communication device 1200 may be a UE and the other one may beanother UE. Alternatively, one of the communication device 1100 and thecommunication device 1200 may be a network node and the other one may beanother network node. In the present disclosure, the network node may bea base station (BS). In some scenarios, the network node may be a corenetwork device (e.g. a network device with a mobility managementfunction, a network device with a session management function, andetc.).

In some scenarios of the present disclosure, either one of thecommunication devices 1100, 1200, or each of the communication devices1100, 1200 may be wireless communication device(s) configured totransmit/receive radio signals to/from an external device, or equippedwith a wireless communication module to transmit/receive radio signalsto/from an external device. The wireless communication module may be atransceiver 1113 or 1213. The wireless communication device is notlimited to a UE or a BS, and the wireless communication device may beany suitable mobile computing device that is configured to implement oneor more implementations of the present disclosure, such as a vehicularcommunication system or device, a wearable device, a laptop, asmartphone, and so on. A communication device which is mentioned as a UEor BS in the present disclosure may be replaced by any wirelesscommunication device such as a vehicular communication system or device,a wearable device, a laptop, a smartphone, and so on.

In the present disclosure, communication devices 1100, 1200 includeprocessors 1111, 1211 and memories 1112, 1212. The communication devices1100 may further include transceivers 1113, 1213 or configured to beoperatively connected to transceivers 1113, 1213.

The processor 1111, 1211 implements functions, procedures, and/ormethods disclosed in the present disclosure. One or more protocols maybe implemented by the processor 1111, 1211. For example, the processor1111, 1211 may implement one or more layers (e.g., functional layerssuch as PHY, MAC, RLC, PDCP, RRC, SDAP). The processor 1111, 1211 maygenerate protocol data units (PDUs) and/or service data units (SDUs)according to functions, procedures, and/or methods disclosed in thepresent disclosure. The processor 1111, 1211 may generate messages orinformation according to functions, procedures, and/or methods disclosedin the present disclosure. The processor 1111, 1211 may generate signals(e.g. baseband signals) containing PDUs, SDUs, messages or informationaccording to functions, procedures, and/or methods disclosed in thepresent disclosure and provide the signals to the transceiver 1113and/or 1213 connected thereto. The processor 1111, 1211 may receivesignals (e.g. baseband signals) from the transceiver 1113, 1213connected thereto and obtain PDUs, SDUs, messages or informationaccording to functions, procedures, and/or methods disclosed in thepresent disclosure.

The processor 1111, 1211 may be referred to as controller,microcontroller, microprocessor, or microcomputer. The processor 1111,1211 may be implemented by hardware, firmware, software, or acombination thereof. In a hardware configuration, application specificintegrated circuits (ASICs), digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs), orfield programmable gate arrays (FPGAs) may be included in the processor1111, 1211. The present disclosure may be implemented using firmware orsoftware, and the firmware or software may be configured to includemodules, procedures, functions, etc. performing the functions oroperations of the present disclosure. Firmware or software configured toperform the present disclosure may be included in the processor 1111,1211 or stored in the memory 1112, 1212 so as to be driven by theprocessor 1111, 1211.

The memory 1112, 1212 is connected to the processor of the network nodeand stores various types of PDUs, SDUs, messages, information and/orinstructions. The memory 1112, 1212 may be arranged inside or outsidethe processor 1111, 1211, or may be connected to the processor 1111,1211 through various techniques, such as wired or wireless connections.

The transceiver 1113, 1213 is connected to the processor 1111, 1211, andmay be controlled by the processor 1111, 1211 to transmit and/or receivea signal to/from an external device. The processor 1111, 1211 maycontrol the transceiver 1113, 1213 to initiate communication and totransmit or receive signals including various types of information ordata which are transmitted or received through a wired interface orwireless interface. The transceiver 1113, 1213 includes a receiver toreceive signals from an external device and transmit signals to anexternal device. The transceiver 1113, 1213 can up-convert OFDM basebandsignals to a carrier frequency under the control of the processor 1111,1211 and transmit the up-converted OFDM signals at the carrierfrequency. The transceiver 1113, 1213 can include an (analog)oscillator, and up-convert the OFDM baseband signals to a carrierfrequency by the oscillator. The transceiver 1113, 1213 may receive OFDMsignals at a carrier frequency and down-convert the OFDM signals intoOFDM baseband signals, under the control of the transceiver 1111, 1211.The transceiver 1113, 1213 may down-convert the OFDM signals with thecarrier frequency into the OFDM baseband signals by the oscillator.

In a wireless communication device such as a UE or BS, an antennafacilitates the transmission and reception of radio signals (i.e.wireless signals). In the wireless communication device, the transceiver1113, 1213 transmits and/or receives a wireless signal such as a radiofrequency (RF) signal. For a communication device which is a wirelesscommunication device (e.g. BS or UE), the transceiver 1113, 1213 may bereferred to as a radio frequency (RF) unit. In some implementations, thetransceiver 1113, 1213 may forward and convert baseband signals providedby the processor 1111, 1211 connected thereto into radio signals with aradio frequency. In the wireless communication device, the transceiver1113, 1213 may transmit or receive radio signals containing PDUs, SDUs,messages or information according to functions, procedures, and/ormethods disclosed in the present disclosure via a radio interface (e.g.time/frequency resources). In some implementations of the presentdisclosure, upon receiving radio signals with a radio frequency fromanother communication device, the transceiver 1113, 1213 may forward andconvert the radio signals to baseband signals for processing by theprocessor 1111, 1211. The radio frequency may be referred to as acarrier frequency. In a UE, the processed signals may be processedaccording to various techniques, such as being transformed into audibleor readable information to be output via a speaker of the UE.

In some scenarios of the present disclosure, functions, procedures,and/or methods disclosed in the present disclosure may be implemented bya processing device. The processing device may be a system on chip(SoC). The processing device may include the processor 1111, 1211 andthe memory 1112, 1212, and may be mounted on, installed on, or connectedto the communication device 1100, 1200. The processing device may beconfigured to perform or control any one of the methods and/or processesdescribed herein and/or to cause such methods and/or processes to beperformed by a communication device which the processing device ismounted on, installed on, or connected to. The memory 1112, 1212 in theprocessing device may be configured to store software codes includinginstructions that, when executed by the processor 1111, 1211, causes theprocessor 1111, 1211 to perform some or all of functions, methods orprocesses discussed in the present disclosure. The memory 1112, 1212 inthe processing device may store or buffer information or data generatedby the processor of the processing device or information recovered orobtained by the processor of the processing device. One or moreprocesses involving transmission or reception of the information or datamay be performed by the processor 1111, 1211 of the processing device orunder control of the processor 1111, 1211 of the processing device. Forexample, a transceiver 1113, 1213 operably connected or coupled to theprocessing device may transmit or receive signals containing theinformation or data under the control of the processor 1111, 1211 of theprocessing device.

In the implementations of the present disclosure, a UE operates as atransmitting device in uplink (UL) and as a receiving device in downlink(DL). In the implementations of the present disclosure, a BS operates asa receiving device in UL and as a transmitting device in DL. In thepresent disclosure, a processor, a transceiver, and a memory, which areincluded in or mounted on a UE, are referred to as a UE processor, a UEtransceiver, and a UE memory, respectively, and a processor, atransceiver, and a memory, which are included in or mounted on a BS, arereferred to as BS processor, a BS transceiver, and a BS memory,respectively.

The AM RLC entity according to the implementation(s) of the presentdisclosure is implemented by the processor 1111, 1211.

The processor 1111, 1211 may be configured to construct M RLC PDUsincluding M RLC SDUs, respectively, before there is a transmissionopportunity. When a transmission opportunity (hereinafter, firsttransmission opportunity) available to the processor 1111, 1211 occurs,the processor may transmit some or whole of the M RLC PDUs. Theprocessor 1111, 1211 may transmit all the M RLC PDUs when the total sizeof RLC PDUs to be transmitted in the transmission opportunity is largerenough to accommodate all the M RLC PDUs and when all SNs of the M RLCPDUs fall within the transmitting window. In some situations, theprocessor 1111, 1211 may transmit only L RLC PDUs in the firsttransmission opportunity, where L<M. For example, if the M RLC PDUsinclude RLC PDU(s) whose SN(s) falls outside of the transmitting window,the processor 1111, 1211 does not submit/transmit the RLC SDU(s) whoseSN(s) fall outside of the transmitting window. The L RLC PDUs have SNsfalling within the transmitting window. The MAC entity configured in theprocessor 1111, 1211 may notify a RLC entity of the first transmissionopportunity, and the RLC entity configured in the processor 1111, 1211may submit only the L RLC PDUs for the first transmission opportunityamong the M RLC PDUs. The L RLC PDUs include respective L RLC SDUshaving lowest L SNs among SNs of the M RLC SDUs included in the M RLCPDUs. Each of the L RLC SDUs may be a (complete) RLC SDU or a segment ofa RLC SDU.

The processor 1111, 1211 may include a poll in at least one RLC PDU(hereinafter, first RLC PDU) among the L RLC PDUs to be transmitted inthe first transmission opportunity. The processor 1111, 1211 may beconfigured to set POLL_SN to SN of the first RLC PDU upon submitting theRLC PDU to MAC. In detail, the RLC entity may include a poll in thefirst RLC PDU among the L RLC PDUs, and start a poll retransmissiontimer upon submitting the first RLC PDU including a poll to MAC. Theprocessor 1111, 1211 may construct a MAC PDU including the L RLC PDUsfor the first transmission opportunity. The processor 1111, 1211 maytransmit (or control the transceiver operably coupled or connected tothe processor 1111, 1211 to transmit) the MAC PDU in the firsttransmission opportunity. The RLC entity may set POLL_SN to SN of thefirst RLC PDU upon submitting the RLC PDU to MAC.

The poll retransmission timer would not be restarted or stopped unlessanother transmission opportunity occurs or the processor 1111, 1211receives a STATUS report comprising a positive or negativeacknowledgement for the RLC SDU with SN equal to POLL_SN. The pollretransmission timer started based on the first RLC PDU may expire astime goes. Expiry of a poll retransmission timer may mean that there isno transmission opportunity between the first transmission opportunityand the expiry of the poll retransmission timer and the processor 1111,1211 have not received a STATUS report comprising a positive or negativeacknowledgement for the RLC SDU with SN equal to POLL_SN.

Upon expiry of the poll retransmission timer, the processor 1111, 1211may determine whether the RLC buffer (e.g. transmission buffer andretransmission buffer) is empty excluding transmitted RLC or RLC SDUsegment awaiting acknowledgment. In this example, the RLC buffer wouldhave at least one RLC PDU since only L RLC PDUs among M RLC PDUs issubmitted and transmitted and there is no other transmission opportunityafter the first transmission opportunity and before the expiry of thepoll retransmission timer. Upon expiry of the poll retransmission timer,the processor 1111, 1211 may determine whether a new RLC SDU can betransmitted. In the implementation(s) of the present disclosure, the newRLC SDU may mean an RLC SDU not transmitted previously or a RLC SDUsegment not transmitted previously. The remaining RLC SDU(s) other thanthe already submitted/transmitted L RLC SDUs among the M RLC SDUs,and/or other RLC SDU(s) having SN(s) higher than the highest SN of the MRLC SDUs could be new RLC SDU(s) available for transmission unless thereis a reason (e.g. window stalling) keeping them from being transmitted.For example, if SNs of the remaining RLC SDUs are outside of thetransmission window, the processor 1111, 1211 may determine that the RLCSDUs in the RLC buffer, which have not been submitted to MAC ortransmitted, cannot be transmitted. In such a case (or in the windowstalling case), the processor 1111, 1211 may determine that no new RLCSDU or RLC segment can be transmitted. The processor 1111, 1211 isconfigured to consider the RLC SDU (hereinafter, second RLC SDU) withthe highest SN among the RLC SDUs submitted to MAC (or among RLC SDUstransmitted to a receiving device) for retransmission when the pollretransmission timer expires and when no new RLC SDU or RLC SDU segmentcan be transmitted. In other words, the processor 1111, 1211 isconfigured to select the RLC SDU with the highest SN among the RLC SDUssubmitted to MAC (or among RLC SDUs transmitted to a receiving device)for retransmission when the poll retransmission timer expires and whenno new RLC SDU or RLC SDU segment can be transmitted. As the latesttransmission opportunity is the first transmission opportunity, thehighest SN among the RLC SDUs submitted to MAC (or transmitted to areceiving side) is the same as the highest SN among SNs of the L RLCSDUs submitted/transmitted in the first transmission opportunity. Inother words, the RLC SDU with the highest SN among the L RLC SDUs isselected as an RLC SDU to be retransmitted.

The processor 1111, 1211 may form a new RLC PDU (hereinafter second RLCPDU) containing the second RLC SDU. The processor 1111, 1211 may formthe second RLC PDU including a poll as well as the second RLC SDU. Theprocessor 1111, 1211 may submit the second RLC PDU to MAC when atransmission opportunity (hereinafter, second transmission opportunity)occurs. The processor 1111, 1211 construct a MAC PDU the second RLC PDU,and transmit (or control the transceiver to transmit) the MAC PDU in thesecond transmission opportunity.

When, upon or while constructing the M RLC PDUs, the processor 1111,1211 may update the state variable TX_Next. TX_Next would hold a valueequal to ‘the highest SN of the M RLC PDUs+1’ right after constructingthe M RLC PDUs. The processor 1111, 1211 may be configured to updateTX_Next whenever the processor 1111, 1211 constructs an RLC PDUcontaining an RLC SDU with SN=TX_Next or the last segment of an RLC SDUwith SN=TX_Next.

As described above, the detailed description of the preferredimplementations of the present disclosure has been given to enable thoseskilled in the art to implement and practice the disclosure. Althoughthe disclosure has been described with reference to exemplaryimplementations, those skilled in the art will appreciate that variousmodifications and variations can be made in the present disclosurewithout departing from the spirit or scope of the disclosure describedin the appended claims. Accordingly, the disclosure should not belimited to the specific implementations described herein, but should beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

INDUSTRIAL APPLICABILITY

The implementations of the present disclosure are applicable to anetwork node (e.g., BS), a UE, or other devices in a wirelesscommunication system.

The invention claimed is:
 1. A communication device configured tooperate in an acknowledged mode (AM) to transmit a data unit in awireless communication system, the communication device comprising: atransceiver; at least one processor; and at least one computer memorythat is operably connectable to the at least one processor and that hasstored thereon instructions which, when executed, cause the at least oneprocessor to perform operations comprising: receiving M radio linkcontrol (RLC) service data units (SDUs) from a Packet Data ConvergenceProtocol (PDCP) layer of the communication device; constructing M RLCprotocol data units (PDUs) for the M RLC SDUs, respectively, where M islarger than 1; based on constructing the M RLC PDUs, submitting, to amedium access control (MAC) layer of the communication device and for atransmission opportunity, only L RLC PDUs, among the M RLC PDUs,corresponding to L RLC SDUs among the M RLC SDUs, where the L RLC PDUscomprise a first RLC PDU having a poll to trigger status reporting at areceiving device; starting a poll retransmission timer based onsubmitting, to the MAC layer of the communication device, the first RLCPDU having the poll; controlling the transceiver to transmit the L RLCPDUs to the receiving device; based on (i) expiration of the pollretransmission timer, and (ii) a state in which no new RLC SDU can betransmitted; selecting, for retransmission, a second RLC SDU having ahighest sequence number (SN) among SNs of the L RLC SDUs submitted tothe MAC layer, where L<M; constructing, based on selecting the secondRLC SDU for retransmission, a second RLC PDU that comprises the secondRLC SDU; and controlling the transceiver to transmit the second RLC PDUcomprising the second RLC SDU.
 2. The communication device according toclaim 1, wherein the operations further comprise: including the pollinto the second RLC PDU.
 3. The communication device according to claim1, wherein the operations further comprise: setting a state variable to1+a highest SN among SNs of the M RLC PDUs, wherein the state variableholds an SN that is to be assigned for a newly generated RLC PDU, andwherein the state variable is updated whenever an RLC PDU, whichincludes an RLC SDU or a last segment of an RLC SDU, is constructed withan SN that is equal to the state variable.
 4. The communication deviceaccording to claim 1, wherein the operations further comprise:constructing a MAC PDU comprising the L RLC PDUs; and controlling thetransceiver to transmit, in the transmission opportunity, the MAC PDU.5. The communication device according to claim 1, wherein the highest SNamong the SNs of the L RLC SDUs submitted to the MAC layer is smallerthan a highest SN among SNs of the M RLC SDUs.
 6. The communicationdevice according to claim 1, wherein the first RLC PDU, having the pollto trigger the status reporting, comprises: at least one field whosevalue indicates whether to trigger the status reporting.
 7. A processingdevice configured to control a communication apparatus to operate in anacknowledged mode (AM) in a wireless communication system, theprocessing device comprising: at least one processor; and at least onecomputer memory that is operably connectable to the at least oneprocessor and that has stored thereon instructions which, when executed,cause the at least one processor to perform operations comprising:receiving M radio link control (RLC) service data units (SDUs) from aPacket Data Convergence Protocol (PDCP) layer of the communicationapparatus; constructing M RLC protocol data units (PDUs) for the M RLCSDUs, respectively, where M is larger than 1; based on constructing theM RLC PDUs and submitting, to a medium access control (MAC) layer of thecommunication apparatus and for a transmission opportunity, only L RLCPDUs, among the M RLC PDUs, corresponding to L RLC SDUs among the M RLCSDUs, where the L RLC PDUs comprise a first RLC PDU having a poll totrigger status reporting at a receiving apparatus; starting a pollretransmission timer based on submitting, to the MAC layer of thecommunication apparatus, the first RLC PDU having the poll; transmittingthe L RLC PDUs to the receiving apparatus; based on (i) expiration ofthe poll retransmission timer, and (ii) a state in which no new RLC SDUcan be transmitted: selecting, for retransmission, a second RLC SDUhaving a highest sequence number (SN) among SNs of the L RLC SDUssubmitted to the MAC layer, where L<M; constructing, based on selectinthe second RLC SDU for retransmission, a second RLC PDU that comprisesthe second RLC SDU; and transmitting the second RLC PDU comprising thesecond RLC SDU.
 8. The processing device according to claim 7, whereinthe operations further comprise: including the poll into the second RLCPDU.
 9. The processing device according to claim 7, wherein theoperations further comprise: setting a state variable to 1+a highest SNamong SNs of the M RLC PDUs, wherein the state variable is updatedwhenever an RLC PDU, which includes an RLC SDU or a last segment of anRLC SDU, is constructed with an SN that is equal to the state variable.10. The processing device according to claim 7, wherein the operationsfurther comprises: constructing a MAC PDU comprising the L RLC PDUs; andtransmitting, in the transmission opportunity, the MAC PDU comprisingthe L RLC PDUs.
 11. The processing device according to claim 7, whereinthe highest SN among the SNs of the L RLC SDUs submitted to the MAClayer is smaller than a highest SN among SNs of the M RLC SDUs.
 12. Theprocessing device according to claim 7, wherein the first RLC PDU,having the poll to trigger the status reporting, comprises: at least onefield whose value indicates whether to trigger the status reporting. 13.A method of transmitting a data unit by a communication deviceconfigured to operate in an acknowledged mode (AM) in a wirelesscommunication system, the method comprising: receiving M radio linkcontrol (RLC) service data units (SDUs) from a Packet Data ConvergenceProtocol (PDCP) layer of the communication device; constructing M RLCprotocol data units (PDUs) for the M RLC SDUs, respectively, where M islarger than 1; based on constructing the M RLC PDU submitting, to amedium access control (MAC) layer of the communication device and for atransmission opportunity, only L RLC PDUs, among the M RLC PDUs,corresponding to L RLC SDUs among the M RLC SDUs, where the L RLC PDUscomprise a first RLC PDU having a poll to trigger status reporting at areceiving device; starting a poll retransmission timer based onsubmitting, to the MAC layer of the communication device, the first RLCPDU having the poll; transmitting the L RLC PDUs to the receivingdevice; based on (i) expiration of the poll retransmission timer, and(ii) a state in which no new RLC SDU can be transmitted; selecting, forretransmission, a second RLC SDU having a highest sequence number (SN)among SNs of the L RLC SDUs submitted to the MAC layer, where L<M;constructing, based on selecting the second RLC SDU for retransmission,a second RLC PDU that comprises the second RLC SDU; and transmitting thesecond RLC PDU comprising the second RLC SDU.
 14. The method accordingto claim 13, further comprising: including the poll into the second RLCPDU.
 15. The method according to claim 13, further comprising: setting astate variable to 1+a highest SN among SNs of the M RLC PDUs, whereinthe state variable holds an SN that is to be assigned for a newlygenerated RLC PDU, and wherein the state variable is updated whenever anRLC PDU, which includes an RLC SDU or a last segment of an RLC SDU, isconstructed with an SN that is equal to the state variable.
 16. Themethod according to claim 13, further comprising: constructing a MAC PDUcomprising the L RLC PDUs; and transmitting, in the transmissionopportunity, the MAC PDU comprising the L RLC PDUs.
 17. The methodaccording to claim 13, wherein the highest SN among the SNs of the L RLCSDUs submitted to the MAC layer is smaller than a highest SN among SNsof the M RLC SDUs.
 18. The method according to claim 13, wherein thefirst RLC PDU, having the poll to trigger the status reporting,comprises: at least one field whose value indicates whether to triggerthe status reporting.
 19. The communication device of claim 1, whereinin the state in which no new RLC SDU can be transmitted: no RLC SDU canbe transmitted which has not already been submitted to the MAC layer.